Using the Nvidia Control Panel you can set what application is using what graphics board.
Anyway, this is not valid for all applications, some of them will attempt to search for GPU's on their own and use the GPU they decide to use.
In the end it all depends on the application you are using, it is not at all a matter of installed boards.
Quadro boards have a lot of professional features unlocked compared to gaming cards, so again it just depends on the software you target. For example, i need to use 20 concurrent H264 video encodings in paralell, then i can only use the quadro because the GTX is locked to 2 paralell streams.
Additionally, depending on the usecase, you can only use some features when there is no display connected to the board.
Again and after all, it all depends on your software. Please edit your question if you have more requirements to add.